Manipulation of plants to alter and/or improve phenotypic characteristics (such as productivity or quality) requires the expression of heterologous genes in plant tissues. Such genetic manipulation relies on the availability of a means to drive and to control gene expression as required. For example, genetic manipulation relies on the availability and use of suitable promoters which are effective in plants and which regulate gene expression so as to give the desired effect(s) in the transgenic plant.
Constitutive promoters are favored in situations where expression in all (or most) tissues during all (or most) times of the plant development is required. The number of constitutive promoters functional in monocotyledonous plants is limited and include the rice actin 1 (Wang 1992; U.S. Pat. No. 5,641,876), CaMV 35S (Odell 1985), CaMV 19S (Lawton 1987), and the maize ubiquitin promoters (Christensen 1996). While several constitutive and tissue-specific promoters from dicotyledonous plants are described by sequence (e.g., the promoter from the caffeoyl-CoA-O-methyltransferase gene from parsley (Grimmig 1997), poplar (Chen 1998) and pine (Li 1999)) only a very limited number has been characterized in heterogenous gene expression. In comparison with dicotyledonous promoters, promoters from monocotyledonous plants are still very limited. It is advantageous to have the choice of a variety of different promoters so that the most suitable promoter may be selected for a particular gene, construct, cell, tissue, plant, or environment. Moreover, the increasing interest in cotransforming plants with multiple plant transcription units (PTU) and the potential problems associated with using common regulatory sequences for these purposes merit having a variety of promoter sequences available.
Root-preferential or root-specific promoters are useful for alteration of the function of root tissue, modification of growth rate, improvement of resistance to root preferred pathogens, pests, herbicides or adverse weather conditions, for detoxification of soil as well as for broadening the range of soils or environments in which said plant may grow. Root abundant or root specific gene expression would provide a mechanism according to which morphology and metabolism may be altered to improve the yield and to produce useful proteins in greater amounts. In particular, root specific promoters may be useful for expressing defense-related genes, including those conferring insectical resistance and stress tolerance, e.g. salt, cold or drought tolerance, and genes for altering nutrient uptake. The number of root preferential and root-specific promoters functional in monocotyledonous plants is very limited. These include the MR7 promoter from Zea mays (U.S. Pat. No. 5,837,848), the ZRP2 promoter of Zea mays (U.S. Pat. No. 5,633,363), and the MTL promoter from Zea mays (U.S. Pat. Nos. 5,466,785 and 6,018,099). Many of these examples disclose promoters with expression patterns confined to a limited number of root tissues. Other fail to provide the root specificity needed for expression of selected genes. It is advantageous to have the choice of a variety of different promoters so that the most suitable promoter may be selected for a particular gene, construct, cell, tissue, plant, or environment. Moreover, the increasing interest in cotransforming plants with multiple plant transcription units (PTU) and the potential problems associated with using common regulatory sequences for these purposes merit having a variety of promoter sequences available.
There is, therefore, a great need in the art for the identification of novel sequences that can be used for expression of selected transgenes in the economically most important monocotyledonous plants, especially in rice and maize. It is thus an objective of the present invention to provide new and alternative expression cassettes for expression of transgenes in monocotyledonous plants, more preferably with the opportunity to modulate the tissue specificity of expression